Silicon-Free SuFEx Reactions of Sulfonimidoyl Fluorides: Scope,Enantioselectivity, and Mechanism

SuFEx reactions, in which an S−F moiety reacts with a silyl-protected phenol, have been developed as powerful click reactions. In the current paper we open up the potential of SuFEx reactions as enantioselective reactions, analyze the role of Si and outline the mechanism of this reaction. As a result, fast, high-yielding, “Si-free” and enantiospecific SuFEx reactions of sulfonimidoyl fluorides have been developed, and their mechanism shown, by both experimental and theoretical methods, to yield chiral products.     

Special Forms of Copolymer Composition Equations

A theoretical explanation is presented for the experimentally observed binary copolymer composition equations in the form of y = Kx^a, where y is the ratio of the numbers of two monomers being incorporated in the polymer, x is the number or concentration ratio of the two monomers in the feed, and K and “a” are constants characteristic of the copolymerization system. The value of “a,” found experimentally, ranges from 0 to near 4. It is shown that the composition equation of this form with a = 0, 1, 2, 3, and 4 can be obtained under various limiting conditions from the conventional copolymer composition equations which take into account the terminal and penultimate effects. This simplification is often accompanied with reduction in the order of Markovian comonomer sequence distribution statistics associated with the original standard composition equations. It is also pointed out that the conventional composition equations can account for y = Kx^a with noninteger “a” for limited experimental ranges of x.     

Combining artificial neural networks and experimental design to prediction of kinetic rate constants

A “soft-modelling” computational approach of artificial neural networks (ANNs) combined with experimental design (ED) has been applied successfully in Chemical Kinetics for the prediction of kinetic rate constants. The system studied comprises two consecutive first-order reactions and the kinetic data were computed determining the values of both rate constants. The kinetic curves were distributed according to an ED, and the central star composite experimental design (CSCED) was chosen as the most appropriate. Computational treatments were performed on synthetic data endowed with noise, after which they were applied to the data measured in an experimental reaction between carbonyl cyanide 3-clorophenylhydrazone with 2-mercaptoethanol, computing the experimental kinetic data of absorbance acquired at 3 wavelengths. The combined ANN and ED approach applied in chemical kinetics proved to be robust and of general applicability and has the advantage of being a “soft-modelling” method such that it was not necessary to solve the system of ordinary differential equations to determine the explicit mathematical function between the data and the kinetic rate constants. Additionally, upon using the CSCED experimental design, it was possible to substantially reduce the number of experiments.     

Silicon‐Free SuFEx Reactions of Sulfonimidoyl Fluorides: Scope,Enantioselectivity, and Mechanism

SuFEx reactions, in which an S?F moiety reacts with a silyl‐protected phenol, have been developed as powerful click reactions. In the current paper we open up the potential of SuFEx reactions as enantioselective reactions, analyze the role of Si and outline the mechanism of this reaction. As a result, fast, high‐yielding, “Si‐free” and enantiospecific SuFEx reactions of sulfonimidoyl fluorides have been developed, and their mechanism shown, by both experimental and theoretical methods, to yield chiral products.     

On the quantum field theory of photoionisation and electron scattering reactions on atoms

Brillouin-Wigner perturbation theory, formulated in the Schrödinger picture of quantum field theory, is employed to derive a perturbative scheme for the scattering matrix for photoionisation and electron scattering reactions on atoms. It is important to note that the intermediate states appearing in this series are physical, i.e. fully correlated, eigenstates of the total Hamiltonian. The scheme is amenable to numerical analysis: The key point is the use of an “energy-optimised”g-Hartree basis which yields an efficient treatment of atomic correlations and makes Brillouin-Wigner and Rayleigh-Schrödinger perturbation theories coincide.     

Expanding the Scope of Arylsulfonylacetylenes as Alkynylating Reagents and Mechanistic Insights in the Formation of Csp2?Csp and Csp3?Csp Bonds from Organolithiums

We describe the unexpected behavior of the arylsulfonylacetylenes, which suffer an “anti‐Michael” addition of organolithiums producing their alkynylation under very mild conditions. The broad scope, excellent yields, and simplicity of the experimental procedure are the main features of this methodology. A rational explanation of all these results can be achieved by theoretical calculations, which suggest that the association of the organolithiums to the electrophile is a previous step of their intramolecular attack and is responsible for the unexpected “anti‐Michael” reactions observed for substituted sulfonylacetylenes.     

微量热法研究单底物酶促反应的产物抑制作用

本文建立了有产物抑制的单底物酶促反应动力学的对比进度方程和热力学的数学模型。根据此模型, 可由反应的热谱曲线方便地解析出动力学参数(K~m, K~i和V~m)和摩尔反应焓(△~rH~m), 并同时确定产物的抑制类型。用微量热法研究了精氨酸酶催化水解L-精氨酸的热动力学, 确定水解产物L-鸟氨酸属于竞争性可逆抑制剂, 298.15K和pH 9.4时L-鸟氨酸与精氨酸酶作用的抑制常数K~i=1.22×10^-^3mol·L^-^1。实验结果验证了本文有产物抑制的单底物酶促反应热动力学研究法的正确性。     

Measures of stochasticity for nonstationary initial preparations of coupled oscillators

The contributions of different eigenstates of a nonlinearly coupled oscillator system to the expansion of a local wave packet are analyzed from an information theoretical point of view. Such a wave packet can be considered as a nonstationary vibrational state of an electronically excited manifold of a molecule after Franck–Condon type initial preparation. The distributions of these contributions are compared to their individual stochastic ideals using Ruch's concept of “mixing distances.” The stochastic ideals are constructed via a probability diffusion process between neighboring states of the original distributions, representing an initial preparation corresponding to a Hamiltonian with only irregular eigenstates. Gaussian minimum uncertainty wave packets as initial states in a two-dimensional nonlinear oscillator system with classically regular and chaotic energy ranges are studied numerically. It is found that distance measures, partly reflecting the “mixing distance” of a distribution from its stochastic ideal, show a large fluctuation in the classical regular energy range and a small fluctuation in the range where most of the classical trajectories move chaotically. This indicates that for this type of initial preparation process the actual location of the initial state in space plays the dominant role for the dynamics in the low-energy range while for wave packets starting near the dissociation energy of the model system this location becomes unimportant.     

540—Evolution with time of the zero-current potential of a gold electrode in Escherichia coli cultures supplied with lipoic acid: Part I. Mathematical modeling and computer simulation

Zero-current potential measurements (gold electrode) are suitable for continuously following the oxidation—reduction reactions of exogenic lipoic acid during Escherichia coli bacterial growth. This paper relates to a mathematical modeling of the experimental time-courses of potential.First, an empirical mathematical relation was obtained in vitro (i.e. in a sterile culture broth) between the zero-current potential and the concentrations of electroactive species that coexist and prevail in vivo (i.e. during the cultures).Secondly, a system of simple kinetic equations was proposed to express the metabolic, physical or chemical processes responsible for the in vivo time evolutions of the concentrations of electroactive species from which the time evolution of the electrode potential during the cultures was obtained. Most of these equations have been standardized by direct measurements. Numerical values could be applied to the remaining parameters of the model by comparing the computer-simulated time-courses of potential with experimental potential—time signals.The model properly fitted the experimental reality. It substantiated a theoretical correlation between the time evolutions of potential and the reductive activity of cultures by means of growth parameters relative to the population of organisms and transport or consumption parameters relative to the bacterial cell.     

Modeling and Simulation of Extraction Flowsheet for FBR Fuel Reprocessing

The present work describes the mathematical basis of a computer code for the analysis of PUREX flowsheet. The model equations have been developed on the basis of the idealized model for mixer settlers. The distribution coefficients relations for U(VI), U(IV), Pu(IV), Pu(III), Ru & Zr and the redox reactions rates of the species involved in U/Pu partitioning are incorporated. The validity of the model equations is tested by carrying out experiments in an ejector mixer-settler with simulated solutions. The stage-wise experimental concentration profiles compare well with the theoretical predictions. An optimum flowsheet for FBR fuels reprocessing has been proposed.     

The Mechanism of N-Heterocyclic Carbene Organocatalysis through a Magnifying Glass

The term “N-Heterocyclic carbene organocatalysis” is often invoked in organic synthesis for reactions that are catalyzed by different azolium salts in the presence of bases. Although the mechanism of these reactions is considered today evident, a closer look into the details that have been collected throughout the last century reveals that there are many open questions and even contradictions in the field. Emerging new theoretical and experimental results offer solutions to these problems, because they show that through considering alternative reaction mechanisms a more consistent picture on the catalytic process can be obtained. These novel perspectives will be able to extend the scope of the reactions that we call today N-heterocyclic carbene organocatalysis.     

Cautions regarding the physical interpretation of statistically based separation of the ortho substituent effect into inductive,mesomeric, and steric components—III : Some remarks concerning the significance of steric effects in acidic and alkaline ester hydrolyses

It is demonstrated that acidic and alkaline hydrolyses of o-substituted benzoates and acidic esterification of o-substituted benzoic acids depend upon inductive, “mesomeric”, and steric effects. The “mesomeric” contribution is essentially connected with the nitro and the methoxy groups exerting special effects. The rate data of some acidic and alkaline reactions which may be regarded as being comparable yielded regression equations indicating that steric effects are the same in both reactions. The Taft-Ingold assumption seems to be correct for these reactions, whereas the averaging procedure applied by Taft is questionable. The results taken as a whole lend strong support to the hypothesis that the so-called ortho effect is essentially connected with the size of the substituents and not strictly electrical in nature.     

Zur Theorie der Chiralitätsfunktionen

The Algebraic Theory of Chirality Functions is derived by means of exclusively qualitative considerations. Hence, the significance of quantitative results is questionable. Moreover the construction of “Näherungsansätze” (”Approximation-Ansatz”), which may be interpreted as semiempirical methods, is achieved on the basis of plausibility and mathematical simplicity. Since physical arguments are not included, the consistency or inconsistency of “Näherungsansätze” with experimental results do not justify direct physical conclusions.     

Kinetics and mechanism of the dehydration reaction of sarcosine to a bislactame through diacyclperoxide intermediate in strong acidic medium

The influence of substitution on the amine functional group of glycine in the permanganic oxidation of such an α‐amino acid in moderately concentrated sulfuric acid medium has been investigated. Reaction products analysis has revealed that contrary to the usual α‐amino acid oxidation product, which is an aldehyde species, a valuable compound, namely 1,4‐dimethylpiperazine‐2,5‐dione, has been obtained as the main product via a cheap, simple, efficient, and novel method. Sarcosine has been chosen as a substituted derivative of glycine, and the kinetics and mechanism of its permanganic oxidation have been investigated using a spectrophotometric technique. Conclusive evidence has proven delayed autocatalytic activity for Mn(II) in this reaction, analogous to some α‐amino acids. It has been revealed that such activity can show up when a certain concentration ratio of Mn(II) to sarcosine is built up in the medium, which we call the “critical ratio.” The magnitude of the latter ratio depends on the sulfuric acid concentration. Considering the “delayed autocatalytic behavior” of Mn(II) ions, rate equations satisfying observations for both catalytic and noncatalytic routes have been presented. The reaction shows first‐order dependence on permanganate ions and sarcosine concentrations in both catalytic and noncatalytic pathways, and apparent first‐order dependence on Mn²⁺ ions in catalytic pathways. The correspondence of pseudo‐order rate constants of the catalytic and noncatalytic pathways to Arrhenius and Eyring laws has verified “critical ratio” as well as “delayed autocatalytic behavior” concepts. The activation parameters associated with both pathways have been computed and discussed. Mechanisms for both catalytic and noncatalytic routes involving radical intermediates as well as a product having a diketopiperazine skeleton have been reported for the first time. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 689–703, 2009     

Kinetic analysis of simple irreversible non-homogeneous reactions

Simple non-homogeneous irreversible reactions between a mobile reactant A, and immobile reactive groups R, in a solid yielding immobile product B, are considered. The possibilities are discussed of analysing such reactions when they are partially rate-controlled by the diffusion of A. It is shown that the effect of diffusion can be approximately described by a single parameter (“kinetic modulus”) up to a fairly marked degree of diffusion control; so that methods of kinetic analysis analogous to those used for reactions where the solid acts merely as a catalyst can be applied. The “effective reaction constant” previously defined for use as a kinetic modulus (analogous to the “Thiele modulus” of heterogeneous catalytic reactions) is considered further here. An improved, experimentally measurable kinetic modulus, based on the distribution of B across the solid, is also defined and studied.     

A contribution to non-equilibrium chemical kinetics. II. Strongly non-equilibrium “hot” reactions in liquids and solids

The method proposed in part I for non-equilibrium chemical kinetics is applied to processes provoked by non-equilibrium assemblies of energetic particles in liquids and solids. The movement of such an energetic particle belonging to a certain energy group is considered as a stochastic process when the direction of the velocity is changed stochastically at each step. On the ground of this consideration a simplified model of such a process is introduced: the stochastic movement of a particle is replaced by the deterministic movement of the corresponding quasi-particle having parameters determined through corresponding averages of the stochastic process. By use of this model, group constants of kinetic equations of our abovementioned work were expressed through parameters of microscopic processes in solids and liquids, and systems of non-equilibrium chemical kinetics' equations were written for different case. The proposed approach also permits us to consider the non-equilibrium of the crystalline lattice created by energetic particles. “Hot spot” reactions were considered as an example and a method to distinguish between direct and “hot spot” reactions was indicated. The proposed approach and obtained kinetic equations can be applied to recoil atoms (ions), fission products, hot particles produced in radiation chemistry, photochemistry, by laser beams, flash-photolysis etc. The destruction of the crystalline lattice by laser beams can also be considered by use of these equations.